X-ray apparatus



Nov. 4, 1952 A. KQNTKE 2,617,047

x-RAY APPARATUS 20g'- Zl l.

Zoff' u' I l@ 2 INTOR.

KUN

- Nov. 4, 1952 K -nQKunrrKE y 2,617,047`

-x-RAY APPARATUS Filed sept. 15, 1949 Mx/W A.y KUNTKE X-RAY APPARATUSNov. 4, 1952 Filed sept. 15, 1949 4 Sheets-Sheet 5 INVENTOR. zmKmK/FNov. 4,` "1952 A. KUNTKE v 2,617,047

X-'RAY APPARATUS Filed Sept. 13, 1949 4 Sheets-Sheet 4 k AAAAI l n'Vllvli n l i foo ' INVENToR. ALFRED KUN/KE AGENT Patented Nov. 4, 1952UNITEDV STATES PATENT OFFICE X-RAY APPARATUS (Cl. Z50-103)' Claims.

This invention relates to X-ray apparatus pro-V vided with automaticcontrol.

The maximum permissible load (number of kw.) of X-ray tubes fordiagnostic plu-poses VariesY with different factors.V such as the sizeof the focal spot, lthe manner in which the heat of the focal spotiswithdrawn-the thermal capacity of the anode and the substance of whichthe anode is made. The maximum permissible load is smaller according asits duration is longer. If a given X-ray tube may be loaded for onesec-` ond with a, maximum power ofv Nikw., a load of one tenth of asecond duration may-be, `for example, 1.4 N kw. but-a load of, say, 5secs. duration must not be in excess of 0.6 N kw.' The number of N mayvary widely forA different types of tubes; as a rule itlliesgbetween 5and 20 but even the factors Varying with time (in the said example 1.4for 0.1 sec. and 0.6 for'5 sec.) vary considerably for thevarioustyp'esof tubes.

Modern X-ray apparatus comprise a controldevice for the load quantitiesof the tube, which automatically adapts the load on the tube to the loadcharacteristic curve, the current -being adjusted as a, function ofY theduration of loading and of the voltage across the tube.' which* isgenerally variable between 50 and 100 kv.A

The requirements of the control can be better visualized with the aidofv Fig. 1 and Fig. 2 of the accompanying drawings whichA areperspective' Views o1" three-dimensional graphs'ofthe load capacity ofan X-ray tube. f

In Fig. 1, the ordinate of each point of an arcuate surface ABCD is ameasureof the maximum current intensity which is permissible at aVoltage and for a, length ofgtime, the values of which are determined bythe distances from the two vertical coordinateA planes. It is desirablethat with the use of the current intensity which is adjustedby theautomatic contrlde'vice, the values determined by this plane should beapproximated to the greatest possible extent. is carried out in practicebyusing a variable resistance included in the. primaryv circuit of thefilament-supply transformer or by connecting into the circuit'a voltagesource which contributes to or counteracts the effect of thelament-sup-Aply transformer. The controlemember of this resistance or the switchesby which this voltage' is connected into the circuit are coupled withthe voltage control-member orvl with the load duration control member orwith both.

As a rule, the control of the current intensity is carried out stepwise.Fig. 1 shows how in the latter case the steps may be chosen,f-;namely inThis' 2 three steps in accordance with the voltage chosenv and in threestep's'in' accordance' Withthe time interval chosen', so` thatthecurrent vintensity may be'adjusted to` nine values' in all.

The eie'ct of the X-rays Ona photographic lm, that'is to say' theblackenhg' 0f the' ln'h'is approximately prp'o'rtionalV to" 'Lt-U4,whereV I is tle'nthsty 'of' the tube Current, 't thedurae tion of theloading arid U the voltage across the X-ray' tube. The factors I t`(expressed in mA'mpsQ/sec.) andUKexpie'ssed' in kv.) are, con`sequently, thel quantities" which determine" the optimum exposure of thefilm.

In the perspective Figure 2, the product'IX't is plotted as afunction'pf the tubfe' Voltage U and the time interval' t. In thisigu'rethe'surface EFGH corresponds to the load characteristic' curve of theX-ray tube. It'niay' be seen from this ligure that the' stepwisecont'rolis assumed to be such that, inacc'rdan'ce' with the shape 'of thesurfaceV EFGrH, on an increase in time interval, the prdu'ctIXtisnot'i'r'l'creasedat' the points of current variation but' instead isdecreased and hence also-the photographic effect of the X-'r'ays emittedby the tube. On an increase'in voltage the product 1X1?, atthe pointsofcurret varia-v tion, falls to a lower' v'ali'fe,"so"that in spite ofthis increase the blackei'ir'ig initially diminishes.

Apart from thesedeiciencie's thereis a fur-l ther one which is duetotevoltag'eloss v6c'curring in the high-voltage geeratr'and" in the supplymains. Even if the v"autorriatic control' werecaried out completely inaccrdance with thesurface ABCD of Fig. l or the surface EFGHof Fig. 2.Jthe voltage loss 1.111 th' apparatus results; in a decrease in tubevoltage, and this aiiects the blackening materially, since the latter isdeter` mined by the Vfmuth' power 0f U- In order to transfer the loadguantitiesofV oneA X-ray apparatus to another it is necessary to knowthe *tube voltages? actually occurring and their Vcorrect adjustment.However, as a Irule, they can .b e deter ith thelu's'eioyf" calibrartioncharacteristic curves only. Attempts) have* oi the resistance. leads tobreak'tlov'v'n"ofA the tube therein. Y but if disturbances .toyoperation oc it is ineii'icient when the supply mains has a highresistance.

It1 has flirtMarmor@r .beensugeested to rrovd an indicating deviceypelfrrnftt xinethe vralirls .of Y the tube voltage -iactuallyoccurring, fibydeducting 3 from the value of the no-load voltage anamount which is proportional to the intensity of the tube current. Theresults thus obtained can only be correct so long as one is concernedwith a voltage loss which is proportional with the current intensity.With a mains supply having an appreciable resistance, such as the ,mainssupplies usually available in practice, this is not the case.

For the same reason compensation of the voltage loss by applying to theprimary circuit a correction voltage which is proportional with thecurrent does not yield satisfactory results. As may be seen from Fig. l,this correction voltage must otherwise be chosen to vary in accordancewith the voltage and time interval chosen. With any known measure ofcompensating or indicating the voltage loss based on the intensity ofthe tube current, it was invariably assumed that the resistance of themains was negligible. In practice, however, this is not so and thereforethe solutions hitherto proposed are not successful.

` The present invention provides a control of improved operation whichcan be provided at low cost. The voltage loss is taken into account andthe invention is based on recognition of the fact that at a given ratiobetween the resistance lying (as viewed from the mains) in front of theautotransformer controlling the voltage and that following thistransformer, the voltage loss is constant throughout the voltagecontrol-range if the load on the tube is kept constant, It has beenfound possible thus to compensate the voltage loss throughout the rangeof voltage-control by increasing the primary voltage of the highvoltagetransformer by an amountvarying with the load.

In order that the invention may be more clearly understood and readilycarried into effect, it will now be described more fully with referenceto Figures 3 to 8 of the accompanying drawings.

The principle of such voltage compensation is set out more fullyhereafter.

Fig. 3 shows the greatly simplified circuit-diagram of an X-rayapparatus, in which T1 is an autotransformer and T2 a high-voltagetransformer. UN designates the mains voltage and RN the resistance ofthe mains as far as the autotransformer, RA designatesrthe resistance ofthe autotransformer transferred to the output side and RH the resistanceof the high-voltage transformer, including that of any rectifying tubesused, transferred to the high-voltage side of the said transformer.

XA=U1/UN represents the ratio of the autotransformer and XH=U2/U1 theratio -of the high-voltage transformer. v Y

The total resistance of the circuit appearing at the high-voltage sideof the transformer T2 is calculated as follows:

If 2R is' plotted as a function of U1 or U2, this gives the sum of aconstant component and a quadratic component RN.X2A.X2H, as shown inFig. 4a. Y

Fig. 4a. shows the control-range which extends, for example, from 50 to100 kv. for U2 and in which the voltage loss'isrequired to be constantat a definite load (kw.). The limit values of this range are I and II.Since the load is required to be constant, the current intensity variesin this range by a factor 2, as indicated in Fig. 4b.

In order that the voltage loss may become con- 4 stant throughout thecontrol-range, the product I XR for point I must first of all be equalto that obtaining for point II. This is ensured at a definite ratio, asis found by calculation, if

R11-Hui@ =15 eiiiozljl (1) Under this condition, if vthe load-is lookedupon as the parameter, a parallel shift of the tube voltages isobtained, as is shown in Fig. 5.

Fig. 6 shows the variation of the auxiliary voltage U as a function ofthe load for a denite, adequately chosen mains constant which is suchthat most mains connections exhibit this constant or else, may bebrought in accordance therewith by use of a ballast resistance. Inpractice the desired result may be obtained by a mains constant of, forexample, l/3802 (ohm/volt2) (l ohm for a 380 volts mains and 0.33 ohmfor a 220 volts mains). The characteristic impedances of the apparatusare purposely chosen to be such that the Equation 1 is fulfilled.

If these conditions are fulfilled, the voltage loss can be compensatedin a simple manner.

Since the load on the X-ray tube is required to vary with the durationof the load, it is only necessary to couple the time adjusting memberwith a corresponding member for controlling the auxiliary voltage. Thismay be seen from Fig. 6. By way of example. the load Nk at the minimumtime of loading to be chosen is such that for compensating the voltageloss the amount dUk must be added. With increase in time the load dropsto that which is associated with the longest time interval and isdesignated N1.. at which the voltage dUL is required to be added forcompensation. .A I

In order that the technical means for carrying out the control may -bereduced in size and the load to be switched may be kept small, thecompensating voltage is resolved into a constant component A and acomponent varying with time between Band +B. This is particularlyadvantageous if two or more tubes of diiferent power are required to beconnected to the supply device. This is set out more fully withreference to Fig. 7. IIt is assumed that for two tubes of different loadcapacity the voltage loss is required to be compensated. Withoutintroducing a great error, the component B, which varies with time, maybe kept constant and the component A or Az may alone be chosen tocorrespond to the tube which is brought into operay tion.

An even more simple explanation will -be given to show that it ispossible for the voltage loss to be kept substantially constantthroughout the control-range. The resistance in front of theautotransformer is assumedto be R1 the mains resistance being`consequently included and the Whole of the resistance following thistransformer, reduced to the primary side of the highvoltagetransformer,r to be R2. If the mains voltage is furthermore'designatedby E and the secondary voltage of the control-transformer by E2, and theprimary and secondary current intensities of the control transformer I1and I2, respectively, the total voltage loss dEz'can be assumed to beapproximately equal to 75;?. where a=E12.Ra/Rr. 1

mamon-'z u When Eil Ais variedfbetweenEis-incanti. Eix';

Ez-I-a/Ez will be` substantially 'f constant; if a=Emm.Em`aX, andconsequently if f RZ/REmaEmax/Ea 2)V Not only for Emln but also for Enixthe voltage loss dE2=NR1/E12(Emin-l-Emax). Between Een and Emax, atE2=\/Emin.'Emax, @E2 haSva minimum Vahle Of NRl/E12.2\/Emln.'Emax. t

For the case considered above thatfEmln'-/2Emax (control between 50.and..1(lfkv.);the ratio between the maximum and minimum-valuesmf; dEz is3:2\/2. Consequently there is only V`a difference of '7% betweenthese-values.- Therfac-tor 15 30.108 which appears in' Formula1 -issubstituted forEmmXEmaxinfForml-ila 2.-'l If the tube voltage isvaried'from'sto /100 lsv-j, maximum value,` which corresponds-with`--35"to'70 kV.eff, Emin Emax=25X1B; Between" 45:and '90 kv. thisbecomes 20X 108. Y

By way of example, a simplied" ycircuit-diagram of an X-ra-yapparatus''according tothe invention is shown in Fig.-8, itbeing assumedthat this apparatus comprises two ltubes of different load capacity.

Firstly provision must be made that theL tube current as a functionofthe lOading-'timeand of the tube voltage exhibits a variation asrepresented, for example, in Fig. 1 'bythe' surface ABCD. For thispurpose both the shaft I for voltage-control andthe shaft'2 for-timecontrol are provided with variable 'resistances 3 and 4, the variationof which is chosen'so as to'fulll this condition.

Furthermore a variable 'resistance-'Beets to connect into thefilament-supply circuit'a-resistance suitable for each o fv the twoLtubes; The filament-supply current forY 'each v`of* the `X-ray tubes I1and I8 `is supplied from the filamentsupply transformer I9. Thelatter isfed in a conventional manner through a voltage stabilizing device 6 froman autotransformer 'I. It is eicient to load the two tubes and-anyfurther tube that may be provided)v in accordance with geometricallyidentical characteristic curves, which'is to be understood to rneanthatwithboth tubes the tube currentis'controlld by the automatic device suchthat at eachloading time the ratio between the loads (kw.).remainsconstant This is advantageous since it permits of the product It(mAmp.sec.) beingl indicated on a single logarithmic scale. Differencesinload'capacy between the tubes are allowed for by shifting .the scaleor the pointer through va distance -thevalu'e of which varies with theratio betweenthelloads;

The autotransformer 1 is connected to the mains 8. A resistance 9 servesto adjust the mains resistance to the desired value. A controlley II]has the function of supplying the correct Voltage to the autotransformerin the event of voltage fluctuations in the mains. The correct voltagemay be read from a voltmeter I I.

The high-voltage generator comprises a transformer I2, the secondaryalternating current of which is converted into direct current byrectifying tubes I3 and supplied at will through arms Ill and I of aswitch to either of the two X-ray tubes I1 and I8.

The auxiliary voltage dU for compensatingthe voltage loss is added asfollows: The component A is taken directly from an auxiliary winding 2U,which is provided on the control transformer. The component B is takenfrom a. winding 22 with. the. use lof;- a control-member :2Iz,xwhich.riscoupled to' .the :time selector.; The..winding.:2.2 isuconnected to thercontrol-transformer..` The component B. isf added through a.transformer 23 to.A the voltagewhichlacts on the primary winding ofthe' high-voltage.transformer. I2.: Thecur.- rent is switched onrand off;by anelectromagnetizcally controlled switch .24', Vtheenergizingcurrent of whichis controlled. by a time switch V25.'

WhatI claimi-s;

1. A: circuit arrangement.; for. energizing;y an X-ray tube. withautomatic `control of tube.- cur.- rent. 'comprising .a low-tensioncircuit; 'for ,-enere gizing the cathode. of the X-ray tube...'includngmeans tofadjust the loading time of..the.tube:for a predetermined time.Ainterval, a separatehighfv tension circuit. having :a given electricalresist.- ance for energizing thel anode ofthe Xl-ray. tube, meansto-couple the highandflow-tensionrcircuits to a sourcev of electrical'power havingan electrical resistance proportional to the electricalresistance of the high-tension circuit =for which the voltage lossacross the tube is' proportional to the input-"power-to the tube, andmeans;-in eluded inthe high-tension circuit for compensating for thevoltage loss f resulting ywithcurrent flow in the high-tensionrcircuitand-from the source comprising `means to.` derive a relatively constantvoltage 'component .proportional tothe voltage appliedfrom the source,Vmeans 'to add the voltage thus derived .to the voltage applied from thesource to thehi-gh-tension circuit, means to derive a voltageproportional to the adjusted loading time ofthe tube, andmeansto add-theVoltage proportionall to the adjusted loading. time to the sum of theapplied voltageandthe voltage proportional to .the applied voltagetothereby adjust theA voltage applied to the ytube tov-the 1=;,^quivalent no-load voltage without compensa- 2.A.fcircuitl arrangementiorenergizingan X-raytube with automatic control. of tube currentr.comprising ar low-tension circuit forenergizing thecathode of the X-raytube-including means to adjust the. loading `time of the tubefor apredetermined time interval, a separate hightensionV circuit includingahigh-tensiontransformer and having a vgiven electricalI resistance for.energizing 'the anode-of the X`rayVV tube, means .to couple'thefhighandlow-tension circuits to a source of electricalpowe-rhaving -agiven-.electrical resistance proportionall to the electrical resistanceof the high-tensionvcircuit for which the voltage loss across the tubeis proportional to thel input power-to the tube,4 and means included-inthe high-tension circuit for compensating for thevoltage-lossresulting/with current ow in the'high-tensioncircuit andfrom the source comprising means to derive a relatively constant voltagecomponent proportional to the voltage applied from the source. means toadd the voltage thus derived to the voltage applied from the source tothe high-tension circuit, an adjustable inductor responsive to theadjustment of said tube timing means coupled to the source of electricalpower for deriving a voltage proportional to the adjusted loading timeof the tube, and means to add the voltage proportional to the adjustedloading time to the sum of the applied voltage and the voltageproportional to the applied voltage to thereby adjust the Voltageapplied to the tube to the equivalent no-load voltage withoutcompensation.

3. A circuit arrangement for energizing an X-ray tube with automaticcontrol of tube current comprising a low-tension circuit for energizingthe cathode of the X-ray tube including means to adjust the loading timeof the tube for a predetermined time interval. a separate hightensionsupply circuit having a given electrical resistance for energizing theanode of the X-ray tube, a common transformer for coupling the highandlow-tension circuits to a source of electrical power having anelectrical resistance proportional to the electrical resistance of thehigh-tension circuit for which the voltage loss across the tube isproportional to the input power to the tube, and means included in thehightension circuit for compensating for the voltage loss resulting withcurrent flow in the hightension circuit and from the source comprising atransformer winding coupled to said common transformer for deriving arelativelyconstant voltage component proportional to the voltage appliedfrom the source through said common transformer in series with saidhigh-tension supply circuit, an adjustable inductor responsive to theadjustment of said tube timing means coupled to said common transformerfor vderiving a voltage proportional to the adjusted loading time of thetube, and a control transformer in the high-tension supply for addingthe voltage proportional to the adjusted loading time to the sum of theapplied voltage and the voltage proportional to the applied voltage tothereby adjust` the voltage applied to the tube to the equivalentno-load voltage without compensation.

4. A circuit arrangement for energizing an X-ray tube with automaticcontrol of tube current comprising a low-tension circuit for energizingthe cathode of the X-ray tube including means to adjust the loading timeof the tube for aipredetermined time interval, a separate high-tensioncircuit having a given electrical resistance for energizing the anode ofthe X-ray tube, means to couple the high-,and low-tension circuits to asource of electrical power including an electrical resistance foradjusting the resistance of said source to a value proportionaluto theelectrical resistance of the high-tension circuit for which the voltageloss across ,the tube is proportional to the input power to the tube,and means included in the high-tension circuit for compensating for thevoltage loss resulting with current flow inthe high-tension circuit andfrom the source comprising means to derive a relatively constant voltagecomponent proportional to the voltage applied from` the source, means toadd the voltage thus derivedto the voltage applied from the source tothe hightension circuit, means to derive a voltage vproportional to theyadjusted loading time of the tube. and means to add the voltageproportional to the adjusted loading time to the sum of the appliedvoltage and the voltage proportional to the applied voltage to therebyadjust the voltage applied to the tube to the equivalent no-load voltagewithout compensation.

5.1K circuit arrangement for energizing an X-ray tube with automaticcontrol of tube current comprising a low-tension circuit for energizingthe cathode of the X-ray tube including means to adjust the loading timeof the tube for a predetermined time interval and means to control thecurrent to the cathode proportional to the adjusted voltage applied tothe tube, a separate high-tension circuit having a given electricalresistance for energizing the anode of the X-ray tube, means to couplethe highand low-tension circuits to a source of electrical powerincluding an electrical resistance for adjusting the resistance of saidsource to a value proportional to the electrical resistance of thehigh-tensionvcircuit for which the voltage loss across the tube isproportional to the input power to the tube, and means included in thehigh-tension circuit for compensating for the voltage loss resultingwith current ow in the high-tension circuit and from the sourcecomprising means to derive a relatively constant voltage componentproportional to the voltage applied from the source, means to add thevoltage thus derived to' the voltage applied from the source to thehigh-tension circuit, means to derive a voltage proportional to theadjusted loading time of the tube, and means to add the voltageproportional to the adjusted loading time to the sum of the appliedvoltage and the voltage proportional to the applied voltage to therebyadjust the voltage applied to the tube to the equivalent no-loadVvoltage without compensation.

ALFRED KUNTKE.

REFERENCES CITED The following references are of record in the file ofthis zpatent:

UNITED STATES PATENTS Number Name Date 2,137,647 Graves Nov. 22, 19382,351,486 Constable et al. June 13, 1944 2,379,125 Weisglass June 26,1945 2,512,193 Zavales June 20, 1950 OTHER REFERENCES A Diagnostic X-RayApparatus With Exposure Technique Indication and Overload Protection byA. Nemet et al., Philips Technical Review, August 1948, pp 37-45.

